Abstract
A balanced homodyne detector, with a maximum common mode rejection ratio and clearance of 75.2 dB and 37 dB, is experimentally obtained with two arbitrary photodiodes of the same model. On the basis of self-subtraction photodetector scheme, we divide the influence of photodiodes on the common mode rejection ratio into two parts, including magnitude and phase of output signal. The discrepancy of quantum efficiency and dark current affects magnitude of output signal of photodiodes, which is compensated by adjusting the splitter ratio. The difference of the equivalent capacitance and resistance affects the phase of output signal of photodiodes, which is compensated by the differential fine tuning circuit and adjustable bias voltage circuit. With these designs, the developed homodyne detector can be used for measuring accurately the squeezed state.
Highlights
Squeezed state of light is an important resource for quantum information processing for continuous variables [1]
The combination of HWP2 and PBS2 is used to generate an optical input linearly polarized at 45◦ injected to electro-optic amplitude modulator (EOAM), so as to measure the common mode rejection ratio (CMRR) of the balanced homodyne detector, the EOAM is modulated by a signal generator connected with its RF input connector
The peak is visible that correspond to the modulation frequency (2 MHz) of loading on the EOAM
Summary
Squeezed state of light is an important resource for quantum information processing for continuous variables [1]. Quadrature squeezed vacuum states are applied to realize quantum teleportation which is a fundamental protocol in quantum information processing [2,3,4]. The fidelity of such protocols is limited by the measured value of squeezing level. It is very important to generate highly squeezed light [5] and to measure accurately the highly squeezed light. A typical method to generate highly squeezed light is utilization of sub-threshold optical parametric oscillator (OPO). By improving the stability of phase locking and reducing the system loss, the factor of 9 dB at 860 nm [6] and the factor of 12.3 dB at 1550 nm [7] quantum noises squeezing of a laser field were observed, respectively
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